From Car and Driver. To sniff out the real-world differences, we tested two Honda Civic sedans, each with the CVT, but one with the 174-hp turbocharged 1.5-liter four-cylinder and one with the 158-hp naturally aspirated 2.0-liter. By the EPA’s measure, the turbo Civic holds a 1-mpg edge on the highway with its 31/42-mpg ratings. On a 300-mile loop of mixed highway, rural, and urban driving, the cars proved equally frugal by averaging 40 mpg. Digging deeper, we measured the steady-speed fuel consumption of the two Civics. Some of our results are astounding, such as the 50-plus-mpg both Civics achieve at 55 mph. The turbo wins across speeds ranging from 30 to 90 mph, with a 6-mpg advantage between 40 and 55 mph. To generate the power required to maintain a particular cruising speed, any engine—small or large—must pump a corresponding amount of air. With equivalent gearing, the smaller engine requires a wider throttle opening to pump the same amount of air as a larger engine. Because pump...